Agricultural products such as plants, fruits, vegetables, cereal grains, in the pre-harvest era, assimilate carbon dioxide, water and other chemicals producing plant structure. These nutrients are energy sources for all living organisms. This process (photosynthesis) also release oxygen into the atmosphere. Plant cells, in both the pre-harvest and post-harvest eras, like animal cells, respire. Cellular respiration described a sequence of chemical reactions wherein oxygen is used in the breakdown of glucose, generating energy (manifested as heat) and exhaling carbon dioxide. The skin or outer surface of the product is a porous barrier through which it breathes. Inside the barrier the humidity is almost 100%, while outside the barrier the ambient humidity is generally lower. This humidity gradient causes a partial vapor pressure gradient from inside the product to the outside, forcing water, oxygen and nutrients to leave the product resulting in drying and early death of the product.
The present invention is predicated on the hypothesis that an inverse relation between respiration rate and pressure exists similar to the direct relation of respiration rates and temperature. Others in the prior art have established that the rate of cellular maturity is a direct function of respiration rate. Thus, for a given temperature, an increase in pressure will retard respiration. However, elevated pressure do not mitigate the effects of temperature but merely superimpose a negative effect bias. However, it should be pointed out that elevated pressures in accordance with the present invention will not offset the effect of elevated temperatures. Conversely, elevated pressures as taught by the present invention in concert with depressed temperatures will serve to augment one another.
In the practice of the present invention, in one of its embodiments, a small positive pressure is imposed on the atmosphere surrounding the product which is sufficient to insure a positive partial vapor pressure gradient from ambient pressure to the internal partial vapor pressure. Such a positive pressure gradient neutralizes the outward diffusion of moisture and nutrients.
Accordingly, one objective of the present invention is to provide a means for preserving agricultural products such as fruits and vegetables, and including cereal grains, without the application of wraps, chemical coatings, chemical preservatives, or fumigants. As mentioned above, the process of the invention may be used independently of, or in conjunction with depressed temperatures.
Any respiratory agricultural product may be preserved at any state from growth through harvest and storage for extended periods of time, by utilizing the teachings of the present invention; specifically by imposing a small positive pressure on the atmosphere surrounding the product, typically about 1-5 psi, sufficient to insure positive partial vapor pressure gradients from ambient pressure to internal partial vapor pressure.
The concept of the invention may be applied both to fixed pressure systems, including plastic bags, metal or plastic containers, and the like, for the household consumer; as well as computerized servo-control systems which monitor and regulate the pressure and gaseous constituents so as to compensate for varying ambient parameters including synthetically imposed depressed temperatures. Transients in ambient parameters adversely affect the partial vapor pressure gradients, and the servo-control system may also provide for modifying, on a time oriented basis, inert gaseous constituents for control and/or eradication of undesirable bacteria and organisms, such control being enhanced when the inert gases are pressurized.
It should also be noted that during the transient period of depressing temperature the negative partial vapor pressure gradient is aggravated. Thus, if ambient temperatures fluctuate (imposed if depressed temperatures are employed) then the resultant fluctuations in pressure gradients can be eliminated by controlling the magnitude of the elevated pressure. Similarly, the pressure gradients are aggravated when the agricultural products are subjected to reduced barometric pressures when transported over mountains, for example. Again, to offset these adverse effects the controlled pressures provided by the system of the present invention should be elevated.
As pointed out above, in order to optimize all of the desired parameters in a commercial system incorporating the concepts of the invention, monitoring and servo-control are required. Current technology employing waxes, wraps, depressed temperatures, and the like, partially addresses some of the parameters. Any one of the aggregate of the prevailing state of the art technology effects, once applied, are fixed. This includes the current employment of depressed temperatures. One of the cardinal improvements of the controlled environment concept of the present invention is the fact that it need not be a fixed control, but a servo-controlled environment employing monitoring sensors feeding a computerized control system.
The process and system of the invention is not intended to be a replacement for refrigeration. However, the system and process of the invention accomplishes much more than mere refrigeration, since it effectively seals into the product all of the constituents in the product, and achieves this without destruction to cellular health or without requiring the use of chemicals.